Botanical/commercial classification: Inter-specific hybrid (Prunus salicianaxc3x97P. persica)/Peach and Nectarine Rootstock.
Varietal denomination: cv. K146-43.
Field of the Invention
Over half of the annual production costs for California peaches involve hand labor for pruning, thinning and harvesting which is done on ladders because of the large size of the trees. It is widely recognized that production costs could be substantially reduced if the size of the trees could be reduced enough to eliminate the need for ladders in the orchard. The benefit of size controlling rootstocks has been clearly demonstrated in apples and revolutionized the apple industries in Europe and the U.S.
The primary factor in limiting the use of size-controlling rootstocks in stone fruit production is the lack of availability of suitable size controlling rootstocks with a wide range of compatibility among cultivars. In particular, there is a tremendous need for size-controlling rootstocks compatible with peach and nectarine.
xe2x80x98K146-43xe2x80x99 is an inter-specific hybrid (Prunus salicianaxc3x97P. persica) rootstock that is graft compatible with peach and nectarine (P. persica) scion cultivars and confers size-control (approx. 40-50%) to the peach scions. xe2x80x98Flavorcrestxe2x80x99 peach, the parent peach trees grown on this rootstock, are productive, smaller and require less pruning than trees grown on standard commercial rootstock (xe2x80x98Nemaguardxe2x80x99).
xe2x80x98K146-43xe2x80x99 is an inter-specific seedling genotype derived from a cross made in 1979 between Prunus salicina (xe2x80x98K47-31xe2x80x99 plum, an un-named selection from the USDA, ARS Fresno breeding program) and Prunus persica (xe2x80x98Flavorcrestxe2x80x99 peach) which is not patented. The seed were stratified germinated in the greenhouse and the seedlings planted in the field in the spring of 1980 at USDA, ARS, Postharvest Quarantine and Genetics Research Unit plots at the University of California research plots at Kearney Agricultural Center, Parlier, Calif. 93648. The plant was subsequently budded in the nursery in 1982 and planted at USDA, ARS, Postharvest Quarantine and Genetics Research Unit in Fresno, Calif. The first propagation trial was done in 1982 from cuttings from the original tree. xe2x80x98K146-43xe2x80x99 was first asexually propagated from hardwood cuttings in Fresno, Calif. and subsequently in Oakdale, Parlier, Davis, and Newcastle, Calif. Only 8.3% of the cuttings grew in this first propagation trial but subsequent propagation trials have resulted in  greater than 80% success. New cultivar xe2x80x98K146-43xe2x80x99, in comparison with the parent xe2x80x98K47-31xe2x80x99, is a peach-plum hybrid and so has intermediate characteristics between typical peach and Japanese plum cultivars. xe2x80x98K146-43xe2x80x99 produces no fruit and is suitable as a rootstock only. The parent xe2x80x98K47-31,xe2x80x99 in contrast, is a Japanese plum (Prunus salicina) and thus has all the characteristics of typical fruiting Japanese plum varieties. The propagaules obtained through succeeding asexual propagation of xe2x80x98K146-43xe2x80x99 retain the new distinctive characteristics and reproduce true to type, as demonstrated in the statistical data in the Tables. Initial screening of xe2x80x98K146-43xe2x80x99 for susceptibility to rootknot nematode indicated that xe2x80x98K146-43xe2x80x99 is mildly susceptible.
In November, 1986, cuttings of xe2x80x98K146-43xe2x80x99 were made and planted in a commercial nursery, budded in the nursery in May 1987, and planted at the University of California, Kearney Agricultural Center in January 1988. This was a large rootstock evaluation trial involving more that 80 potential peach rootstock genotypes. The peach scion cultivar used in this trial was O""Henry. After 7 years of collecting field data in this trial, xe2x80x98K146-43xe2x80x99 was selected for further replicated field productivity trials based on its ease of propagation from cuttings, lack of root suckering, compatibility with peach scions and major size-controlling characteristics. Crop productivity of the O""Henry scion cultivar grown on xe2x80x98K146-43xe2x80x99 was excellent considering the reduced tree stature.
xe2x80x98K146-43xe2x80x99 was propagated again by taking cuttings in November 1994 and planted in a commercial nursery, budded in the nursery in June 1995, and planted at University of California, Kearney Agricultural Center in February 1996. This was a large, replicated field productivity trial involving the eight best potential rootstock genotypes from the 1987 trial. The peach scion cultivars for the main part of this trial were xe2x80x98Flavorcrestxe2x80x99 and xe2x80x98Loadelxe2x80x99. After eight years of collecting tree performance data, xe2x80x98K146-43xe2x80x99 stands out as a rootstock that has major size-controlling potential (tree size equal to 50-60% of trees on the standard industry rootstock, xe2x80x98Nemaguardxe2x80x99) and would be acceptable for commercial use. Additional field trials in growers"" orchards have been initiated and to date these trials corroborate previous findings.